This is not hardware bug, why - because this shader work without problems in same AMD hardware in OpenGL.

OS Windows10, AMD drivers latest, everything latest, tested on two PC

Examples(exe) linked in end of this post. (code do not have validation errors at all)

Problem is :

1. using something more complicated then single linear function in AMD SPIR-V shader, with single exit(single return for whole logic) result UB or unpredictable result. Having any code after first single return function will result UB.